Final answer:
A. afarensis and A. africanus had postcranial features suggesting both arboreal and bipedal capabilities, with A. afarensis characterized by particularly long arms and curved fingers and toes, and A. africanus having a larger cranial capacity and robust arm bones.
Step-by-step explanation:
The postcranial morphology of the hominid species Australopithecus afarensis and Australopithecus africanus provide important insights into their locomotion and lifestyle. A. afarensis, dating from 3.9 to 2.9 million years ago (MYA), had long arms and curved finger and toe bones, suggesting arboreal habits alongside a bipedal gait inferred from the pelvic structure. A. africanus, living between three and two million years ago, had a slender build and exhibited bipedalism but also had strong arm bones indicating time spent in trees. Its endocranial capacity was larger than that of A. afarensis, at approximately 500 cubic centimeters. A. afarensis and A. africanus are both classified as gracile australopiths, with characteristics such as smaller canines and molars compared to apes and prognathic jaws. These features, alongside postcranial evidence, highlight adaptations for bipedal locomotion as well as arboreal activity, reflecting the transitional nature of these species in human evolution.